Hearing instruments, such as hearing devices or hearing aids, are often equipped with a multi-microphone system in order to provide directional information of the sound.
In such a directional mode of the hearing instrument, usually two microphones are located at the hearing instrument in a predefined distance from each other.
Especially for hearing devices of the type of in-the-ear (ITE) or completely-in-the-canal (CIC), there is only little space available for arranging the microphones. Even though, the two microphones, usually two electrically identical microphones, have a different acoustical behavior.
Especially the feedback stability and maximum stable gain are depending on the actual microphone location in relation to the venting of the hearing instrument housing, the pinna or other environmental influences caused by the physics of the user of the hearing instrument. Therefore, even if the distance between two technically identical microphones is very small, the feedback stability and maximum stable gain are different for those two microphones.
In EP 1 221 276, which is incorporated herein by reference, a method for adapting a hearing device and a hearing device with two microphones for directional-use is described. To allow the use of such a hearing device either in the left or the right ear of a user of this hearing device, the use of a switching unit to switch the connecting outputs of the microphones to the digital signal processing unit is proposed. Thus, the forward and backward location of the microphones within the hearing device in relation to the front of the head of the user may be adapted and thus the hearing device may be used either for the left or the right ear of the user, providing correct directional information.
Thus, this document teaches a predefined operational connection of multiple microphones to a digital signal processing unit.
In EP 1 309 225, which is incorporated herein by reference, a method for determining the feedback threshold of a microphone in a given location or position respectively within a hearing device and therefore the determination of the maximum gain for this microphone in a given acoustical setup is provided.
This method may be used for limiting the maximum gain for a specific microphone or to determine the value of the maximum gain for a specific microphone for providing feedback stability of the hearing instrument concerned.
It is an object of the present invention to provide a method of adjusting a hearing instrument with at least two microphones for the omni-directional mode.